[time-nuts] Characterization of Oscillator w/ HP5345a

John Miles jmiles at pop.net
Tue Jan 12 03:03:00 UTC 2010


Unfortunately the 5345A's resolution (2000 ps single-shot) is going to be
too coarse to allow you to characterize any decent OCXO or GPSDO at short
timescales.  Even a 5370's ADEV floor takes about 30 seconds to reach 1E-12.
You'll need to build a dual-mixer or ADC-based front end for your counter.

It's good that you have the 11/12 options on the 5345A, though -- they are
uncommon, and make the counter a lot more useful.  It's not the right
instrument for GPSDO optimization but it's fine for long-term drift
monitoring of unstabilized OCXOs.  (TI.EXE doesn't support the 5345A yet,
but it will.)  You should get a National Instruments GPIB adapter if you
want to use my software with it, as the 5345A's weird multiple-address
scheme isn't compatible with the Prologix abstraction layer in my library.

The good news is that you probably don't actually need a cesium reference.
You can use an LPRO-101 or other inexpensive rubidium standard to tweak your
GPSDO's parameters at timescales below a couple thousand seconds, which is
where the tweaking is actually necessary.

-- john, KE5FX


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of John Foege
> Sent: Monday, January 11, 2010 4:54 PM
> To: time-nuts at febo.com
> Subject: [time-nuts] Characterization of Oscillator w/ HP5345a
>
>
> Hello all,
>
> I am new to the world of time-nuts. I am therefore new to the world of
> precision timing/oscillators and the likes. I am learning as I go. One
> project that I am keenly interested in for use in my lab, is a 10MHz
> GPSDO. Obviously this will be useful to me as a starting project as I
> delve into this hobby. It shall also serve useful as reference for my
> freq. counters or any other equipment that needs an accurate timebase.
> I imagine it will also provide a good reference signal for use in
> various HAM radio related projects.
>
> I recently acquired an HP5345a counter with the 4ghz plugin and it
> appears to also have Opts. 11 and 12. It appears to have 3 GPIB
> connectors on the rear panel. I was wondering what kinds of cool
> things I can do with it; specifically could I characterize a GPSDO
> that I am building? Is there software that exists, perhaps John Miles'
> freeware GPIB programs that work with a Prologix interface, etc?
>
> My concern is that I dont have a cesium reference to feed into the
> counter. Therefore I do not have a source that is at least an order of
> magnitude more stable. So what, if anything could I do?
>
> Any ideas? Any suggestions for this project? I intend to build
> something quite similar to:
>
> http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm
>
> I have 2 Jupiter GPS units in my possesion already and the next step
> is to acquire a good OCXO somewhere (eBay from China most likely).
>
> I thank everyone in advance for any suggestions.
>
> Sincerely,
>
> John Foege
> KB1FSX
>
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